The production of cycloalkyl-aromatic compounds via hydroalkylation of benzenes and/or alkylbenzenes, and/or via alkylation of benzenes and alkylbenzenes with cyclic olefins, is an emerging technology. For instance, the hydroalkylation of benzene forms a composition comprising the cycloalkyl-aromatic compound cyclohexylbenzene, as well as other cycloalkyl-aromatic compounds such as methylcyclopentylbenzene and di-cyclohexylbenzene as byproducts. Such a hydroalkylation is described in numerous references, for instance as part of an integrated process for the production of cyclohexanone and/or phenol. See, for example, U.S. Pat. No. 8,247,627 and WIPO Patent Publication No. WO 2015/094530.
Other exemplary processes include hydroalkylation of alkylbenzenes such as toluene and/or xylene to form multi-ring aromatic compounds such as (methylcyclohexyl)toluene and/or (dimethylcyclohexyl)xylene, as described, e.g., in U.S. Patent Publication No. 2014/0275606. Such compounds, it is disclosed, are capable of being further processed to form additional multi-ring aromatic compounds such as methyl-substituted biphenyl compounds (including by dehydrogenation).
The present inventors have recognized that many of the aromatic compounds, and particularly multi-ring aromatic compounds such as those produced in the exemplary processes noted above, may be recovered and used in other applications suitable for aromatics fluids, such as agricultural solvents and high-temperature heat transfer fluids in solar energy applications. Such aromatics fluids are typically sourced from reformate fractions produced during the refining of crude oil and gas hydrocarbons. Such aromatics fractions may be characterized as set forth, e.g., in U.S. Pat. No. 5,459,122, as having a naphthenebenzenes and dinaphthenebenzenes content of at least 50 wt % based on the aromatics fraction. Examples of aromatics fluids currently used in industry include agricultural solvents such as Aromatic 100, Aromatic 150, and Aromatic 200 fluid products, available from ExxonMobil Chemical Company. For instance, the Aromatic 200 fluid products typically may comprise approximately 25 to 30 components, with some of the principle components comprising fused-ring aromatics such as various alkyklnaphthalenes (e.g., 2-methylnaphthalene, 1-methylnaphthalene, 2-ethyl-naphthalene, dimethyl naphthalenes, and trimethyl naphthalenes); as well as alkylbenzenes.
Unconventional sources for blend components and/or substitutes of such aromatics fluids, such as cycloalkylaromatics formed in the aforementioned hydroalkylation processes, may provide attractive alternatives for aromatics fluids, and/or for blending components for use in aromatics fluids, in addition to (or instead of) the traditional reformate fractions.
Similarly, such processes may provide attractive alternatives for high-temperature heat transfer fluid (HTHTF) components, such as biphenyl, terphenyl, and other substituted or unsubstituted multi-aryl compounds useful in, e.g., solar energy harvesting applications.
Several commercially available heat transfer fluids are known to contain biphenyls, terphenyls, and related compounds. For example, Dowtherm™ systems marketed by Dow Chemical Company reportedly contain biphenyls in combination with diphenyl ether. As another example, U.S. Pat. No. 5,075,022 discloses systems containing terphenyls. One drawback for systems containing no-substituted biphenyl is gradual decomposition to (environmentally unfriendly) benzene with long term aging and use.
Some additional references of interest in this regard include: U.S. Pat. Nos. 3,356,486; 4,810,279; 5,459,122; 5,972,971; and 6,797,193; as well as U.S. Patent Publication No. 2005/0215433, Japanese Patent Nos. 05-212705 and 52-038005; and L. Moens and D. Blake, Mechanism of Hydrogen Formation in Solar Parabolic Trough Receivers, NREL Technical Report NREL/TP-510-42468, February 2008.